Reinforced grinding wheels and reinforcement network therefor



N 1969 J. ROBERTSON, JR 7, 8 REINFORCED GRINDING WHEELS ANDREINFORCEMENT NETWORK THEREFOR Filed June .14, 1965 3 Sheets-Sheet 1 anA.

N 11, 1969 J. ROBERTSONyJR 3,477,180

REINFORCED GRINDING WHEELS AND REINFORCEMENT NETWORK THEREFOR Filed June14, 1965 3 Sheets-Sheet 2.

INVENTOR. JOHN ROBERTSON, JR.

" Filed June 14, 1965 Nov. 11, 1969 BER 5 JR 3,477,180

REINFORCED GRINDING WHEELS AND RHiNFORCEMENT NETWORK THEREFOR v 3Sheets-Sheet 3 INVENTOR.

JOHN ROBERTSON, JR N BY United States Patent US. Cl. 51-206 2 ClaimsABSTRACT OF THE DISCLOSURE A rotatable abrasive article having areinforcing network formed of a yarn made from continuous fiber glassfilaments, the yarn being spirally wound about the axis of rotation ofthe article and including a plurality of circumferentially spacedradially extending bands of high tensile strength material disposedacross the spaced spiral turns and bonded thereto to complete thenetwork.

The present invention relates to the improvement of rotatable moldedarticles, such as abrasive grinding wheels and the like by incorporatingtherein one or more networks of a special configuration which may bemanufactured economically and which provides strength even when thewheel is worn and subjected to normal operating conditions.

Grinding wheels of the resinoid bonded type are in widespread use ascutoff and snagging wheels. They are generally used without any coolantand rotated at relatively high speeds. The operating conditions to whichthese grinding wheels are subjected frequently cause the development ofradial cracks in the wheels which materially reduce the strength of thewheels and create a safety hazard to operating personnel and to themachine itself in the event of breakage or disintegration of thegrinding wheels.

Several reinforcing techniques have heretofore been proposed tostrengthen the abrasive structure against likelihood of breaking due tocentrifugal forces. These techniques include imbedding, woven cloth orscreen-like discs, rings, polygons, and short or elongated fibers in thegrinding wheel during the forming process. The materials used haveincluded hard and soft metals and glass, nylon and other fibers.

Abrasive wheels are commonly manufactured by bonding abrasive particlesor grains with resin or comparable material which is otherwise inert andcan be dissipated as the abrading material is progressively worn. Amajor problem encountered in the attempted reinforcement of sucharticles is that of securely integrating the reinforcing elements withthe composite material of the wheel without at the same time sacrificingstrength. For example, a closely woven cloth mesh used to develop morepowerful restraining forces will not be as well penetrated by and lockedwith the composite abrasive material as a looser weave mesh particularlyin cases where the particle sizes are large. On the other hand a looserweave mesh tends to reduce the strength available from the reinforcingfabric or network.

Alternate layers of fiber glass cloth have been employed but the use ofsuch cloth in alternate layers in order to increase the strength of thegrinding wheel to any acceptable degree results in impairment of thegrinding eificiency of the wheel and increases the cost of the wheelmaterially.

In accordance with the present invention, these difliculties are avoidedand significant improvements in wheel strengths and in the ease andeconomy of abrasive wheel manufacture are realized by forming areinforcement web from a band of a plurality of substantially continuous3,477,180 Patented Nov. 11, 1969 glass or other high tensile strengthfilaments into a generally spiral formation by a substantiallycontinuous forming process, thereafter incorporating one or more of suchreinforcement webs into the binder and abrasive mix in the mold and thenbaking or curing the combination to form a solid wheel. This provides anadvantageous distribution of bands interlocked with the molded abrasivematerial, the distribution of which promotes substantial increases instrength and freer cutting action without interference by the materialof the web.

One object of this invention is to provide a novel reinforcing networkwhich, when imbedded in a rotatable molded article, such as a grindingwheel, substantially increases the strength thereof.

Another object is to provide a reinforcement web for such articles whichis economical to manufacture.

A further object is to provide a novel method for the manufacture ofreinforcement webs for rotatable molded articles such as abrasivewheels.

Yet another object is to provide a geometrical pattern for a reinforcingnetwork that extends to a point near the periphery of the grinding wheelto reinforce the wheel but which does not detract from the grindingefficiency of the wheel as the diameter thereof decreases exposingportions of the reinforcing network.

A still further object of the present invention is to provide animproved rotatable reinforced molded abrasive wheel incorporatingtherein a reinforcing web to provide a wheel of high strength, safeoperation, high durability, high grinding efficiency and of economicalmanufacture.

In one embodiment, the foregoing objects and advantages are achieved byemploying a reinforcing network, preferably made from a multifilamentsubstantially continuous strands of glass fibers which are arranged in agenerally spiral formation having a plurality of turns whichprogressively increase in size from the interior toward the periphery ofthe web and eventually the rotatable molded article or grinding wheel.According to a preferred embodiment, the generally spiral turns aresecured together in predetermined spaced relationships by a plurality ofradially extending bands which are bonded to the turns at theircrossover sites by a resinous material which also imparts stiffness tothe web when it cures or sets thereby to provide a reinforcement webwhich is self-sustaining and may be incorporated into the mix for themolded abrasive wheel easily and economically.

In one aspect the method comprises forming a band of glass or otherhigh-tensile-strength filaments into a generally spiral formation bymechanical means, thereafter extending another band of glass or otherhigh-tensile-strength filaments diametrically of the web of generallyspiral turns from a first point near the periphery of the web to asecond point near the opposite side of the periphery, thencesubstantially peripherally of the web for a short distance from saidsecond point, thence diametrically of the web again, and thenceperipherally of the web, and repeating these steps until the desirednumber of radially extending bands have been provided, and thereafterbonding said radial bands to the generally spiral bands at theircross-over sites thereby to provide a reinforcement web which isself-sustaining and stiffened for ease and economy of use in themanufacture of grinding wheels.

Other objects and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, wherem:

FIG. 1 is a plan view of a cutoff grinding wheel embodying thisinvention;

FIG. 2 is a section taken on the lines 2-2 of FIG. 1;

FIG. 3 is a perspective of apparatus suitable for forming a band ofhigh-tensile-strength filaments into generally sprial formation;

FIG. 4 is an enlarged vplan view of certain of the elements of theapparatus of FIG. 3;

FIG. 5 is a side elevation of the elements of FIG. 4;

FIG. 6 is a plan view of the elements of a reinforcement web and certainapparatus elements at a further stage in the method of manufacturing it;and

FIG. 7 is a side elevation of the web and apparatus elements of FIG. 6.

Referring to FIGURES 1 and 2, the grinding wheel, indicated by thenumeral 8, is shown in dot dash and the reinforcement web is shown infull lines. The grinding wheel has a hole 9 at the center and it is madeof abrasive particles and a binder which comprises resin with the webimbedded therein. The web consists of a band or yarn 10 of substantiallycontinuous filaments of fiberglass arranged in a generally spiralformation having a plurality of turns which progressively increase insize from the central hole to the periphery of the web. A plurality ofradially extending elements 11 formed of yarn, also preferably made ofsubstantially continuous fiber glass filaments, extend from the centralorifice nearly to the periphery of the wheel.

The grinding wheel is made by any conventional method, for example bymixing abrasive particles with a dry powdered binder such as a resin,placing the mixture and one or more webs in a suitable mold pressing thecontents of the mold and heating and curing the combination to form asolid annular article.

The apparatus shown in FIGS. 3 to 5 may be used to form a substantiallycontinuous band of high tensile strength material into a generallyspiral formation having a plurality of turns which progressivelyincrease in size from the interior toward the periphery of the web.

Continuous lengths of glass fibers, or other suitable hightensile-strength-filaments, are wound on supply rolls 13 and 14 whichare rotatably supported on the bench extension 16. In one embodiment ofthis invention making use of glass fiber material to make a reinforcingweb for a snagging wheel, 204 continuous individual glass filaments mayconstitute a single end or strand for example, with 72 of such ends orstrands constituting a single band. In the embodiment illustrated twobands are shown, 10A and 10B, and as they are drawn towards the spiralforming assembly they are merged into a single yarn 10 by their passagepartly around a guide pulley 17 which is rotatably mounted on thevertical bracket 18.

A second pulley 19 is mounted below the first pulley and it forces theband 10 to travel through a pool of bonding resin 20 within thecontainer 21. The adjustable platform 23 supports the resin container atthe desired position for impregnation of the glass fiber yarn with theresln.

The impregnated yarn is brought out of the resin pool over a thirdpulley 24 and the excess resin is removed by a wiper 25 through whichthe band passes. The wiper comprises a bracket mounted holder lined withfelt or similar material to exert a gentle squeezing action causing theexcess resin to fall back into the container. Preferably the resin usedis the same as that used for bonding the abrasive particles in theultimate grinding wheel structure, one example comprising a phenolformaldehyde resin, in powder form, which has been dissolved in alcohol.

The apparatus for arranging the yarn 10 into a generally spiralformation comprises a circular table 31 slid ably keyed to the upper endof shaft 32 (FIG. 5) which is rotated by a variable speed reductiondrive unit 34 supported by the bench 15.

The workholder 35 is detachably supported on the table 31 by a pair ofpins 36 secured to the table and passing through orifices in theworkholder 35, thereby insuring that the workholder will be rotated bythe table.

A threaded rod 37 has one end mounted for rotation in a bearing 38 andits other end mounted for rotation by the reversible variable speedreduction drive unit 39.

The guide rod 40 is rigidly mounted in horizontal position by means ofthe tubular member 41 and the vertical strut 42 which is secured to thebench 15.

A pulley supporting bracket 45 has an interiorly threaded passage whichreceives the threaded rod 37 and a second passage which slidablyreceives the guide rod 40. It carries a guide roller or pulley 48 whichis rotatably mounted by means of a spindle 49.

The helical spring 33 presses upwardly against the driven table 31 andprovides moderate friction between the workholder 35 and the guideroller 48. As the table 31 and the threaded rod 37 are rotated, thepulley 48 is caused to rotate and friction between the pulley 48, yarn10 and the surface of the workholder 35, draw the yarn 10 forwardly fromthe spools l3 and 14. The combination of the rotary movement of the worksupport 35 and the rotation of the driven rod 37 cause the guide 45 andguide roller 48 to move from left to right looking at FIG. 5 and thus toform the yarn 10 into a generally spiral formation on the surface of theworkholder 35 having turns which progressively increase in size.

The somewhat tacky resin causes the yarn to remain in the position onthe surface of the workholder where it is applied by the guide roller48.

After the spiral pattern has been formed on the surface of theworkholder, the yarn 10 is cut and the workholder is removed from thetable 31 and placed on the stationary table 50 as shown in FIGURES 6 and7. The stationary table 50 is provided with a plurality of pins 51 whichproject upwardly from its surface. The radial yarn elements 11 are thenformed by extending a single band of substantially continuous glassfilaments, or other hightensile-strength material, from a first point 55near the periphery of the web of the spiral turns diametrically to asecond point 56 near the opposite side of the periphery of the web,thence substantially peripherally of the web to a third point 57 andthence diametrically of the web to a fourth point 58 near the Oppositeperiphery thereof and thence peripherally to a fifth point 59. Thisoperation is repeated until the desired number of radial yarn elements11 have been formed and laid in engagement with the yarn 10 forming thespiral element; see for example the complete pattern of FIG. 6. Duringthis operation the pins 51 serve to retain the radial yarn elements inthe desired positions and also to form the short circumferentialstretches 60 of yarn.

The continuous yarn which forms the radial yarn elements 11 may beimpregnated with resin prior to application to the spiral turns or itmay constitute an untreated yarn of fiberglass filaments. In the lattercase, a suitable adhesive, such as phenolic varnish, may be applied tothe radial yarn elements 11 especially at the cross-over points of theradial and spiral yarn elements.

After the network of FIG. 6 has been completed, the phenolic varnish orthe resin impregnant is partially set or cured so the yarn will bejoined together at the crossover points and the yarn stiffened. This maybe accomplished by placing the assembly of FIG. 6 in an oven, oralternatively the web may be set or cured with the aid of a hot air jet.

After the web has been partially set and stiffened, it may be removedfrom the pins 51, a central hole may be cut to suit the hub of the wheelwhich is to be formed and the circumferential portions 60 of the bandcut away so that the radial yarn elements project only slightly beyondthe outermost spiral turn as shown in FIG. 1.

The reinforcement web then is in condition for placement in the moldwith the binder-abrasive mix and a composite grinding wheel made in themanner described above.

It should be understood that it is unnecessary to use two pieces of yarn10A-10B to form the single yarn element 10, and that either a singlesupply such as 13 may be used or two or more supplies may be used.

Furthermore, the yarn and the yarn 11 may be formed of a plurality ofglass fiber yarn, for example 3, which are twisted or braided to formthe yarn utilized for making the spiral turns and the radial elements.

It is also unnecessary to impregnate the yarn 10 with resin prior to itsapplication to the surface of the workholder 35. Instead of impregnatingthe yarn, it may be surface treated with an adhesive such as phenolicvarnish and the varnish partially dried or set before the yarn 10 isapplied to the surface of the workholder so it will remain in theposition where it is applied.

While the grinding wheel shown in the drawing utilizes only onereinforcing web, the invention contemplates that a plurality of spacedsubstantially parallel webs may be used, depending upon the thickness ofthe wheel and the amount of reinforcement desired.

While the spiral turns are spaced a uniform distance apart in theembodiment which is illustrated, it is within the scope of thisinvention to vary such spacing, for example the turns at the center maybe closer together where the stresses in the wheel are higher.

The thicknesses of cutoff wheels are considerably smaller than ofsnagging wheels but webs embodying this invention are suitable for usein both types of wheels. The cutoif wheel shown in FIGURES 1 and 2 mayfor example be one that is 8 in diameter, 0.158" thick and has a centralhole 1 in diameter, whereas one example of a snagging wheel consists ofa wheel 24" in diameter, 3" thick with a central hole 12" in diameter.Accordingly, to adequately reinforce a snagging wheel it would benecessary to use a plurality of reinforcing webs and the pulley 48 wouldcommence laying the spiral band outwardly from the center of theworkholder 35 to provide a central orifice. It is contemplated that morethan one web may be used in making cutoff wheels also.

As one particular example of the use of my invention, cutoff wheels weremade by cold pressing a mixture consisting of 48% by volume of 24 gritalumina abrasive and 42% by volume of phenolic resin bonding materialstogether in a mold at 160 tons of pressure. The pressed wheels beforecuring had a porosity of 10% by volume, and were 8 7 in diameter by .145thick with 1" diameter center holes.

Spiral reinforcing webs as disclosed herein, each consisting of 168%" ofglass yarn having 44 strands of 204 continuous filaments per strandtwisted together, Specification ECG 150 4/11, commercially availablefrom Owens Corning Fiber Glass Corporation, were placed one on each sideof the pressed green wheels. The wheels each with a spiral web on eachof its sides, were placed between pressure plates and cured in an ovenfor four hours at 175 C.

After curing, the wheels were trued to 8- /6" in diameter and coated onboth sides with a resin binder consisting of 100 parts of BakeliteBRL3794 epoxy resin and 37 parts of ZZL 0803 or other suitable hardener,such as are available from Union Carbide. The resin binder furtherpenetrated the remaining loose glass filaments and was cured in an ovenfor one hour at 125 C. Upon curing of the binder the glass filamentswere securely bound together and the yarn of each web was secured morefirmly to the bonded abrasive mass. The wheels then average .161 of aninch in thickness.

Wheels made in the above manner were tested and were found to be muchsafer and stronger than non-reinforced wheels of comparable size. Thespiral web reinforced wheels were speed tested to destruction andaveraged 13,900 r.p.m. which is an average increase of 1,400 r.p.m.above the speed at which comparable non-reinforced wheels are destroyed.The spiral web reinforcing not only enables the wheels to be run safelyat higher speeds but also provides a higher factor of safety at normaloperating speeds.

It should be noted that the method of this invention does not involveforming the fiberglass yarn in any relatively sharp acute angles andconsequently there is no possibility that the filaments will be crackedor broken and their strength impaired either by the formation of thespiral turns or in forming the radial yarn elements.

From the foregoing description, it will be apparent to persons skilledin the art that this invention provides a novel reinforcing networkwhich when imbedded in a rotatable molded article, such as a grindingwheel, substantially increases the strength thereof, that the resultantarticle has high grinding efficiency and is economical to manufacture.It will also be apparent to persons skilled in the art that thisinvention provides a novel method for the manufacture of reinforcementwebs which is economical and which produces webs which are easy to useduring the manufacture of grinding wheels embodying them.

It should be understood that the specific embodiments and methods hereindescribed have been presented by way of disclosure rather thanlimitation and that various modifications, substitutions andcombinations may be effected without departure in spirit or scope fromthis invention in its broader aspects.

I claim:

1. A reinforced molded abrasive wheel comprising: a substantiallyannular body of abrasive particles secured together by a bindermaterial; at least one reinforcement web embedded within said body, saidweb comprising a substantially continuous band of high-tensile-strengthfiber glass material arranged in a generally spiral formation, insubstantially a single plane, having a plurality of spaced turns whichprogressively increase in size from the interior towards the peripheryof the wheel; a plurality of spaced radially extending elements of hightensile strength fiber glass material disposed in substantially a singleplane across the turns and bonded to the continuous spiral band at aplurality of crossover sites.

2. A reinforcement web for a molded article intended to be rotated abouta center, comprising: a substantially continuous band ofhigh-tensile-strength fiber glass material arranged in a generallyspiral formation in substantially a single plane, having a plurality ofspaced turns which progressively increase in size from the interiortowards the periphery of the web; a plurality of spaced radiallyextending bands of high-tensile-strength fiber glass material disposedin substantially a single plane across the turns and bonded to thecontinuous spiral band at a plurality of crossover sites.

References Cited UNITED STATES PATENTS 228,257 6/ 1880 Hart 51-206699,302 5/ 1902 Fowler 51206 1,860,224 5/ 1932 'Schumacher 51-2063,123,948 4/1964 Kistler 5 l-204 3,141,271 7/1964 Fischer 51-2063,208,838 9/ 1965 Fischer 51206 3,262,230 7/ 1966 Seymour 51-2063,315,418 4/ 1967 Zawodni 51-206 ROBERT C. RIORDON, Primary Examiner D.G. KELLY, Assistant Examiner

